There is increasingly a consumer demand for food products which may be prepared quickly and with guaranteed results. There are on the market a number of quick cooking rice products whose cooking time is substantially lower than that of ordinary rice. In general, this is achieved by precooking the rice. The precooking step results in the absorption of water by the rice so that its moisture content rises from around 12% to 14% by weight for uncooked rice to around 60% by weight. It is then necessary to remove this absorbed water so as to bring the moisture content back to its original level. This drying step must be carried out carefully in order to avoid tainting the rice and is usually achieved by heating or freeze drying.
Often, the speed of subsequent cooking of the treated rice is enhanced by breaking up the granule structure, for example by puffing the cooked grain, flattening between rollers, freeze drying or freezing and thawing.
The main quick cooking rice products currently on the market are produced as follows. "Minute Rice" (General Foods) is produced by sequentially cooking, draining, granulating, drying, rolling and further drying. "Quick Rice" (Uncle Bens) is produced by sequentially cooking, draining, freezing, thawing, and drying. Other commercial products are produced by sequentially cooking, draining, drying, granulating, rolling and drying. Freeze drying is an expensive technique but is used in certain applications, notably for army field rations, calling for reconstitution simply by the addition of water.
However, since all these processes involve a cooking step and a subsequent drying step, they require a high energy input and the product is consequently expensive. Moreover, specialised expensive apparatus is generally required.
Australian patent specification No. 244,945 proposes the production of a quick cooking rice by contacting the rice with air at a temperature of 205.degree. to 315.degree. C. for a short time of 10 to 40 seconds. The apparatus used in this proposal is described in Australian patent specification No. 242,588. In fact, it seems that this process has never been put into commercial use. Experiments show that rice treated as described in these patents is unsuitable for use since the rice is not treated homogeneously, some rice being undertreated and other rice being scorched.
U.S. patent specification No. 2,992,921 describes an apparatus for heat treating brown rice in a fluidised bed. The rice is fed onto a perforated belt which is indexed under a conical chimney and hot air passed through the perforations to lift the rice off the belt. After a short time, the hot air is interrupted, the rice falls back onto the belt and the belt is indexed under a further chimney. Here cold air is passed through the rice. Not only is this apparatus complex with a large number of moving parts but it is found that the rice so treated shows unacceptable variations in the degree of heat treatment.
The present invention seeks to mitigate these disadvantages.